In the field of the so-called “laminated ceramic component/substrate” provided with a capacitor, a resistor, or wiring in its interior, high-frequency dielectric materials, which are ceramic materials comprising not less than 95% of alumina as a main component and silica, alkaline earth metal oxides and the like, have hitherto been used. For such high-frequency dielectric materials, the firing temperature should be one thousand and a few hundred degrees Celsius. Accordingly, high-melting point materials such as tungsten and molybdenum have been used as an internal conductor.
In recent years, however, there is an increasing demand for a technique which can realize transmission of microwave or milli-wave zone signals with low loss. This demand has led to a tendency toward the use of, for example, silver (Ag) or copper (Cu) having lower electric resistance than tungsten and molybdenum as an internal conductor. In general, in high-frequency dielectric materials which are co-fired with the internal conductor, high-frequency dielectric materials which can be sintered at a temperature below the melting point of the internal conductor material should be used. Since silver, copper and the like have a lower melting point than tungsten and molybdenum, high-frequency dielectric materials, which can be sintered at a temperature below the temperature required in the case where tungsten or molybdenum is used as the internal conductor, should be used. For example, when high-frequency dielectric materials are co-fired with silver as the internal conductor, the high-frequency dielectric materials used should be those that can be fired at a temperature satisfactorily below 962° C., i.e., the melting point of silver, for example, at a temperature of about 900° C. Such ceramics are called “low temperature co-fired ceramics” (LTCCs), and various composition systems have recently been proposed.
Among low temperature co-fired ceramics, for example, a system comprising BiNbO4 and V2O5 added as a sintering aid to BiNbO4 has hitherto been proposed as materials having high relative permittivity (referred to also as ∈r) and quality factor (referred to also as Q value; a reciprocal number of dielectric loss angle tanδ) and a resonance frequency temperature coefficient (referred to also as TCF or τf, or referred to simply as temperature coefficient) close to zero (0). This system has high-frequency (GHz zone) properties of a relative permittivity of about 45, a Q value of about 4000, and a TCF value of −10 to +40 ppm/° C. Further, as described in Japanese Patent Laid-Open No. 44341/2000 (patent document 1), a material of 45 mol % ZnNb2O6+55 mol % TiO2+a few percent of sintering aid has been developed which has a relative permittivity of 42, a Q value of 4000 to 20000, and a TCF value of −1 to +12 ppm/° C. (a value around 6 GHz).
In these materials, when a production process in which, after pre-firing of a high-frequency dielectric material, a silver paste is printed and baked on the pre-fired material, is used, the resultant assembly can exhibit functions as dielectric material/insulator without any problem. The adoption of co-firing of the high-frequency dielectric material with the internal conductor, for example, the adoption of a method comprising preparing a sheet using the high-frequency dielectric material, printing and stacking a fine wiring of a silver paste onto the sheet, and co-firing the high-frequency dielectric material with silver, however, poses a problem that silver dissipation due to a reaction of silver with ceramic components or very rapid diffusion of silver into the ceramic components occurs and makes it impossible to form wirings as designed. Various studies have been made on material systems where the dissipation of silver is not substantially observed. However, there is no report about a material which can realize firing at a temperature of 900° C. or below white having a high relative permittivity, a Q value exceeding 1000 in GHz zone, and a TCF property value close to zero (0).
[Patent document 1] Japanese Patent Laid-Open No. 44341/2000